German Patent Application No. 196 19 354 describes a method of operating a control unit having a control function and having a programmable memory device for storing control function programs and control function data required to execute the control function. The method described here is characterized in that certain automatic control data not belonging to control function programs and control function data is entered into the memory device at predetermined locations within the memory device in conjunction with entering the control function programs and control function data. Depending on whether the certain automatic control data is stored at the predetermined locations, the control unit is then operated. Since the automatic control data in the aforementioned document is not part of the control function programs and control function data actually to be stored, i.e., the useful data, but instead is provided as a separate bit pattern, it requires additional memory. A review of the automatic control data then prevents an attempt to execute useful data that is not properly accessible or is not stored in the memory device. The cause and/or the time of occurrence of the useful data that is not accessible or is not stored is not recorded. The proposed method is also used only with memory devices or parts thereof that must be erased completely before programming. No means is provided for simply reprogramming the data, i.e., writing over the data. The goal here is to perform a type of emergency control program despite programming that is defective in part, using only the functional data to do so.
In addition, German Patent Application No. 196 23 145 describes a method of operating a control unit having a memory device programmable by a programming device, where the contents of the memory device are erased and written over each time, executing a section of the program for data processing and using data. The method described here is characterized in that at least either the program section for data processing or the data is made available so that it requires modification before being used to erase or write over old data. This modification is carried out only when it has been found that a jump in the program section for data processing has taken place or will or can take place as intended. Since the data to be entered instead of the data already entered is modified, a malfunction or a function failure due to an interruption or disturbance in the programming is unavoidable. This is all the more so since the interruption or disturbance is not noted in the memory. The modification in the above-mentioned document is used to simply and reliably prevent unintentional erasing and/or overwriting of data stored in a programmable memory device. However, this does not make it possible to secure the programming when this has already been initiated, i.e., the modification has already been carried out. Any malfunction or interruption occurring then results in data loss, i.e., incomplete programming and thus functioning of the control unit fails or becomes defective.
For these reasons, among others, it has been found that these methods are incapable of yielding optimum results in all regards.